gcc: define __block when block support is enabled

This mimics the behaviour in clang and lets us build cleanly
the libdispatch port on platforms where the base gcc is still
the default compiler.

Bump __FreeBSD_version for ports.

Tested by:	theraven
MFC after:	3 days
Rework the iSCSI PDU transmit code to avoid lock contention and coalesce
PDUs before sending.

Sponsored by:	The FreeBSD Foundation
Change kernel/rootfs hints to use search patterns instead of absolute
locations.
Remove dead code.

MFC after:	1 week
Sponsored by:	Yandex LLC
Remove unused variable.

MFC after:	1 week
Sponsored by:	Yandex LLC